Somatomedin and other factors in serum and tissues that stimulate cell growth and replication will be studied in regard to their dependence on pituitary growth hormone and their specificity of tissue targets. The nature of an inhibitor that appears in culture medium will be examined. The spargana growth factor produced by the larvae of Spirometra mansonoides which we recently found to compete with pituitary growth hormone for receptor sites will be further studied in regard to biological effects, species range of activity, chemical nature and relation to growth hormone. Studies involving extraction, purification and clinical use of human pituitary hormones will be continued.